This invention relates to a power supply assembly for a semiconductor integrated circuit tester.
A conventional semiconductor integrated circuit tester that is used in conjunction with failure analysis equipment for probing the semiconductor material of an integrated circuit device while stimulating the device comprises a test head that interfaces to a device under test (DUT) through a device interface board (DIB) and pin electronics that transmit stimulus signals to and monitor response from the DUT. The tester also includes a device power supply that is connected to power supply pins of the DUT for supplying regulated DC voltage to the DUT for operating the DUT during the test.
Several trends in design and manufacture of integrated circuits influence the magnitude of the current drawn by an integrated circuit device. In particular, as advances in fabrication technologies allow integrated circuit devices to be made with smaller features, integrated circuits can be designed to include larger numbers of transistors. As the number of transistors increases, the power demands of the IC device will generally increase; and if the operating voltage of the IC device remains the same, the current drawn by the IC device will increase.
However, the reduction in size of features of IC devices allows the devices to operate at higher frequencies and as operating frequencies of integrated circuits increase, the operating voltage of the integrated circuits generally decreases. Consequently, the reduction in size of device features may lead to increase in current both because of an increase in the number of transistors and because of a reduction in operating voltage. Many testers are designed for concurrent testing of several IC devices. When an IC tester is to test concurrently several low voltage, high current IC devices, it must be able to provide a substantial amount of current to the devices under test.
A typical IC device including a large number of clocked gates draws a relatively high current during the first part of a clock cycle, when many transistors are actively switching, and a relatively low current during the latter part of the clock cycle, after the transistors have switched. Further, the amount of current drawn can vary from cycle to cycle depending mainly on how many transistors switch during each particular cycle.
In at least one known IC tester, the tester's device power supply is positioned remote from the test head and force and return terminals of the power supply are connected through cables to respective conductive power distribution blocks adjacent the DIB. Each power distribution block includes an array of spring probe pins (commonly known as pogo pins) that engage power supply contact pads of the DIB and the DIB includes conductive traces that connect the power supply contact pads to the power supply (Vcc and ground) terminals of the DUT. In this known tester, there is a relatively long conductive path between the terminals of the device power supply and the VCC and ground terminals of the DUT, and these long conductive paths may have substantial inductance and resistance. The inductance and resistance of the power supply path results in a change in voltage drop across the path impedance when the current supplied to the DUT changes, and this change in voltage drop results in a change in voltage between the Vcc and ground terminals of the DUT. Changes in operating voltage between the power supply terminals of the DUT must be kept within specified limits in order for the DUT to operate properly. As the operating voltage of ICs decreases, acceptable variations in operating voltage also decrease.
One way to reduce the magnitude of variation in power supply voltage is to connect voltage regulating capacitors to the power supply lines at a location as close as possible to the DUT. However, as the demand for current increases and the tolerance for variation in power supply voltage decreases, the capacitors that are needed to provide the necessary voltage regulation become impractically large.